1. Field of the Invention
This invention relates to epoxy resin compositions and more particularly, to epoxy resin compositions capable of yielding cured products which have not only good mechanical, electrical and waterproofing characteristics, but also a low stress property, a good crack resistance and a low moisture absorption without lowering a glass transition point and which are particularly suitable for encapsulating or packaging electronic and electric parts.
2. Description of the Prior Art
The resins currently used for encapsulating or packaging electronic or electric parts are thermosetting or thermoplastic resins including, for example, epoxy resins, silicone resins polybutadiene, polyurethanes, phenolic resins and the like. These resins are selectively used depending upon the manner of application or the purpose.
Among these resins, the epoxy resins have widely used in large amounts because of their good mechanical and electrical characteristics, heat resistance, adhesiveness and moldability. For encapsulators of semiconductor elements such as diodes, transistors, ICs, LSIs and the like, which are technically advanced drastically in recent years, the epoxy resins outrival the other resins in view of the better characteristics.
However, since the current tendency of the electronic parts is to make them thinner or smaller in size with an increasing degree of integration, the characteristics required for encapsulators become more severe. Under these circumstances, existing epoxy resins are not necessarily satisfactory.
The characteristics required as encapsulators for the recent semiconductor elements include a higher purity, higher electric characteristics, a more shortened molding cycle ensuring improved productivity, a higher heat transmittance for heat dissipation, a low stress property for mitigating a physical stress on the elements, and a better crack resistance sufficient to suffer a severe heat cycle or shock.
In order to improve these characteristics, the present inventors proposed in Japanese Patent Publication Nos. 60-56171 and 61-48544 epoxy resins in which organopolysiloxanes or copolymers of organopolysiloxanes and aromatic polymers are formulated.
However, the improvement of the characteristics can be realized by the above proposed resin compositions, but a further improvement is desirable so as to satisfy the recent severe requirements. In recent years, as the package is made thinner, it is not unusual to adopt a method of immersing a package itself in a solder melt. In this method, when the package absorbing moisture is subjected to soldering, the moisture in the resin may instantaneously vaporize to break the package. In this sense, it is required to have a low moisture absorption characteristic.